I have a Mapletree Ultra 4A phono preamp that just doesn't give me enough output. The question is can I modify the linestage section for more gain or replace it with something else? Possibly just use the phono portion with a different linestage that has more gain? I'd consider dumping the whole thing but I like the sound of it and the fact that I have a dozen 12SC7 tubes and a box of 50) 1634 tubes.
Since the phono stage has about 50dB gain, you must be using a low output mc cartridge.
The phono stage gain cannot be increased, but you could try a step up transformer.
More line stage gain will only increase the noise level, but perhaps that would be an
acceptable compromise. Can you post the schematic?
The phono stage gain cannot be increased, but you could try a step up transformer.
More line stage gain will only increase the noise level, but perhaps that would be an
acceptable compromise. Can you post the schematic?
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I don't know if it would be proper to post a Maple tree schematic since it has a copyright. This would be probably be a violation of forum policies/rules. I could however send a copy via email to you.
I'm using a MM cartridge with a output of 2mv.
I'm using a MM cartridge with a output of 2mv.
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I'm tempted to build the Maple tree phone section on a small chassis so I can use it with my 6AU6/5687 Aikido linestage. The Aikido would have tons of gain.
There's no way it lacks enough gain unless the circuit has been changed.
What is the line stage, and the power amp and speaker system?
I'll send you my email.
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I was using it in conjunction with my Allen model 75 mono tube amps and my Klipsch cornwall clone speakers.
Input signal directly into the EF86 input of the Allen's bypassing the 12AY7 input.
Input signal directly into the EF86 input of the Allen's bypassing the 12AY7 input.
Google 'Mapletree Ultra 4A schematic' and you get the manual, which includes schematic.
Do you have the Allen's volume control turned up all the way? Of course the speakers are very efficient.
There should be no problem with the phono output level in this system.
Can you do some simple gain tests on the preamp and power amp?
Can you play the turntable in another system and verify that its output level seems normal?
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I have tested the amps and they are spot on for output. Bypassing the 12AY7 input stage does lower the signal which is to be expected.
The turntable output is lower than I had expected when run thru other systems. It to be blunt seems anemic.
I'll borrow another cartridge from someone and try it and see if there is a change.
The turntable output is lower than I had expected when run thru other systems. It to be blunt seems anemic.
I'll borrow another cartridge from someone and try it and see if there is a change.
Idea on checking the phono preamp section for gain....
What is I used a step up transformer in reverse? I have a transformer with a turns ratio of 17.25-1 and if I hooked it up backwards and fed a sine wave into it of .05175 V P-P if my math is correct I would get .003 volts from the primary to feed into the phono preamp section. I have a decent Krohn-Hite signal generator but I doubt I can get it down to 3mv to feed the phono input directly also I thought the transformer would isolate.
Would this work?
What is I used a step up transformer in reverse? I have a transformer with a turns ratio of 17.25-1 and if I hooked it up backwards and fed a sine wave into it of .05175 V P-P if my math is correct I would get .003 volts from the primary to feed into the phono preamp section. I have a decent Krohn-Hite signal generator but I doubt I can get it down to 3mv to feed the phono input directly also I thought the transformer would isolate.
Would this work?
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Would it not tell me if the phono section was outputting its rated 50db gain level with 3mv input? or is the original testing done with the inverse filter for lack of better terms?
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_I_ would say the Phono gain is less than 32dB; I get 32.5dB at 1kHz with a 12AX7 model which is a bit higher gain than 12SC7. See attached. That's the extra gain from Phono to Line, the way we used to figure it.
The Line gain is rated 18dB and looks like 20+dB. Added to phono gain this offers maybe 50dB gain from Phono to output.
50dB is 1:316, so a 5mV needle signal comes up to 1.58V which "should" be ample for most power amps, though the Volume knob has to be full up to get loud. (In this topology there is NO objection to running VOL as high as it takes.)
The Line gain is rated 18dB and looks like 20+dB. Added to phono gain this offers maybe 50dB gain from Phono to output.
50dB is 1:316, so a 5mV needle signal comes up to 1.58V which "should" be ample for most power amps, though the Volume knob has to be full up to get loud. (In this topology there is NO objection to running VOL as high as it takes.)
Attachments
Ok,
I guess I will be content to run the volume near max level then and live with it unless I take the output level from the phono section and run it into a different line stage with more gain.
I guess I will be content to run the volume near max level then and live with it unless I take the output level from the phono section and run it into a different line stage with more gain.
How about using a little silicon? Build a tiny pre-preamp having 5X gain and flat frequency response, from a super low noise opamp chip like the LT1115 (for moving magnet cartridges) or the AD797 (for moving coil cartridges). Install this between the cartridge and the existing phonostage.
Since 5X == +14dB, your new phonostage gain is (14 + 32) = 46dB , and your phono-to-output gain is now (14 + 50) = 64 dB.
Since 5X == +14dB, your new phonostage gain is (14 + 32) = 46dB , and your phono-to-output gain is now (14 + 50) = 64 dB.
The RIAA networks could be changed to avoid/reduce the significant loss of gain in the resistive divider R121-R122
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how about using a SUT?, it is a fairly simple and elegant way to 'amplify' the signal before it enters the preamp.
50dB as about as much as one really would want to go with a tube preamp lest you end up with too much noise from the tube circuitry!
50dB as about as much as one really would want to go with a tube preamp lest you end up with too much noise from the tube circuitry!